This invention relates to digital TDMA (Time Division Multiple Access) cellular radio mobile telecommunications systems. More specifically, the present invention is directed towards apparatuses and mobile stations for providing packet data communications services in current TDMA cellular systems.
Mobile data communication is rapidly becoming one of the fastest growing segments of the mobile communications market. Independent market studies predict several million users in Europe by the year 2000. A strong driving force is the fast growing portable personal ("laptop", "palmtop" and "notebook") computer market and the need for flexible wireless data communications it creates. This market force is further emphasized by the emerging new communication-centered devices, commonly referred to as "Personal Digital Assistants" or "Personal Communicators". Target applications include:
The wide range of standard business applications today predominantly used across fixed data networks, such as electronic mail and host computer/data base access. PA0 Specialized mobile data applications including vehicle fleet control and road transport informatics. PA0 Fixed wireless applications, including remote monitoring and control applications, and credit card verification and similar financial transaction applications. PA0 Possible new applications as a result of the convergence of the two enabling technologies of new personal computing/communicating devices and efficient and widely available mobile data communications. PA0 Provide packet mode data services based on shared packet data radio channels optimized for packet data (exploiting the bursty nature of most data communications applications) to achieve spectrum efficiency and cost effectiveness. PA0 Provide industry standard network services, including standard connectionless network (datagram) services and, depending on market requirements, standard connection-oriented network (virtual call) services e.g. to provide transparent X.25 connectivity. PA0 Provide performance (packet transfer delays) comparable to what is provided by current fixed networks, to allow existing standard applications to be used without modification. PA0 Provide broadcast and multicast services to support specialized mobile applications. PA0 GSM (Global System for Mobile communication) PA0 Systems with a GSM type of architecture but operating in other frequency bands, such as the 1800 and 1900 MHz bands, including PCN (Personal Communications Network) in Europe and PCS (Personal Communications Services) in the U.S.A. PA0 The North American D-AMPS (Digital Advanced Mobile Phone Service) system. PA0 The Japanese PDC (Personal Digital Cellular) system.
To support this variety of applications in a cost effective manner, a mobile data network should:
Providing the packet data services on a cellular system platform offers potential advantages in terms of widespread availability, possibility of combined voice/data services, and comparatively low additional investments by capitalizing on the cellular infrastructure. Of particular interest are current TDMA cellular systems, through their spectrum efficiency and world wide penetration. Examples of potential TDMA platforms include:
However, the data services provided by or proposed for cellular systems in general are with few exceptions based on circuit mode of operation, using a dedicated radio channel for each active mobile user. The exceptions include the packet data concepts described in the following documents:
a) U.S. Pat. No. 4,887,265 and Proc. 38th IEEE Vehicular Technology Conference, June 88, Philadelphia (U.S.), pages 414-418: "Packet Switching in Digital Cellular Systems".
These documents describe a cellular system providing shared packet data radio channels, each one capable of accomodating multiple data calls. A mobile station requesting packet data service is assigned to a particular packet data channel using essentially regular cellular signalling. The system may include Packet Access Points (PAPs) for interfacing with packet data networks. In that case, each packet data radio channel is connected to one particular PAP and is thus capable of multiplexing data calls associated with that PAP. System initiated handover (handoff) is employed, to a large extent similar to the type of handover used in the same system for voice calls. A new type of handover is added for handling situations when the capacity of a packet channel is insufficient.
b) U.S. Pat. No. 4,916,691.
This document describes (for one of the embodiments) a new packet mode cellular radio system architecture, and a new procedure for routing (voice and/or data) packets to a mobile station. Base stations, public switches via trunk interface units, and a cellular control unit are linked together via a wide area network. The routing procedure is based on mobile station initiated handover and on adding to the header of any packet transmitted from a mobile station (during a call) an identifier of the base station through which the packet passes. In case of an extended period of time between subsequent user information packets from a mobile station, the mobile station may transmit extra control packets for the sole purpose of conveying cell location information. The cellular control unit is primarily involved at call establishment, when it assigns to the call a call control number. It then notifies the mobile station of the call control number and the trunk interface unit of the call control number and the identifier of the initial base station. During a call, packets are then routed directly between the trunk interface unit and the currently serving base station.
c) Cellular Digital Packet Data (CDPD) System Specification, Release 1.0, July, 1993.
CDPD is a new concept for providing packet data services, utilizing available radio channels on current Advanced Mobile Phone Service AMPS systems (i.e. the North American Analog Cellular System). CDPD is a comprehensive, open specification endorsed by a group of U.S. cellular operators. Items covered include external interfaces, air interfaces, services, network architecture, network management, and administration. The CDPD system specified is to a large extent based on an independent infrastructure. Common denominators with AMPS systems are limited to utilization of the same type of radio frequency channels and the same base station sites (the base station itself, used by CDPD, is new and CDPD specific), and employment of a signalling interface for coordinating channel assignments between the two systems. Routing a packet to a mobile station is based on, first routing the packet to a home network node (home Mobile Data Intermediate System, MD-IS) equipped with a home location register (HLR), based on the mobile station address; then, when necessary, routing the packet to a visited, serving MD-IS based on HLR information; and finally transferring the packet from the serving MD-IS via the current base station, based on the mobile station reporting its cell location to its serving MD-IS.
d) ETSI (European Telecommunications Standards Institute) T Doc SMG 4 58/93, Feb. 12, 1993: "Packet Radio in GSM"; and "GSM in a future competitive environment", seminar, Helsinki, Oct. 13, 1993: "A General Packet Radio Service Proposed for GSM".
These documents outline a possible packet access protocol for voice and data in GSM.
e) ETSI T Doc SMG 1 238/93, Sep. 28, 1993: "Packet Data over GSM Network".
This document describes a concept of providing packet data services in GSM based on first using regular GSM signalling and authentication to establish a virtual channel between a packet mobile station and an "Agent", handling access to packet data services. With regular signalling modified for fast channel setup and release, regular traffic channels are then used for packet transfer.
Of the above documents, documents d) and e) directly relate to a TDMA cellular system. Documents d), although outlining a possible organisation of an optimized shared packet data channel, do not deal with the aspects of integrating packet data channels in a total system solution.
The concept described in document e), being based on using a "fast switching" version of existing GSM traffic channel, has disadvantages in terms of spectrum efficiency and packet transfer delays (especially for short messages) compared to a concept based on optimized shared packet data channels.
The system described in documents a) is data call oriented and based on using system initiated handover in a similar way as for regular voice calls. Applying these principles for providing general purpose packet data services in a TDMA cellular system would imply spectrum efficiency and performance disadvantages. For example, system initiated handover in GSM is based on allocating 1/26 of a traffic channel capacity during a call for signalling related to monitoring and controlling signal quality (for a single mobile station) in preparation for a possible handover.
The systems described in documents b) and c) are not directly related to the specific problems of providing packet data services in TDMA cellular systems.
To summarize, there is a need for a system concept for providing general purpose packet data services in TDMA cellular systems, based on providing shared packet data channels optimized for packet data.